Gear milling tool assemblies have been developed for the manufacture of gears, such as bevel and hypoid gears with curved flank lines. Many face mill cutter assemblies, for example, include a disk-shaped cutter head that attaches to the milling machine and a plurality of cutting blades that are coupled to the cutter head. The cutting blades are arranged about a center point of the cutter head at varying radial positions. The cutting blades are arranged in groups, with usually two or three cutting blades per group. In two-blade groups, the blade pair comprises an inner cutting blade and an outer cutting blade. In the three-blade group, a “bottom” cutting blade is included with the inner and outer cutting blades. Typically, one tooth slot is formed in the work piece with each plunge of the cutter assembly. The cutter assembly is then withdrawn, and the work piece is indexed to the next tooth slot position in order to form the next tooth slot as is widely known in the art.
During typical face hobbing processes, the cutter and the work piece rotate independently in a timed relationship with each other, thereby allowing continual indexing of the work piece and continual formation of each tooth slot of the gear. Each successive group of cutting blades passes through successive tooth slots with each blade in the group forming a cut completely along the longitudinal portion of the tooth slot. Thus, in most face hobbing processes, a single plunge of the cutting tool results in all tooth slots of the work piece being formed.
In many prior art gear milling tool assemblies, the cutting blades are elongate stick-type members that are disposed in slots in the disk-shaped cutter head. The cutting blades are typically made from bar stock high speed steel (HSS). To form a gear within high tolerances, it is preferable if each of the cutting blades are uniform. However, after prolonged use of the gear milling tool assembly, one or more of the cutting blades wear, and the cutting blades typically require sharpening. However, sharpening the cutting blades can be time-consuming and costly.
U.S. Pat. No. 6,609,858 to Francis et al. discloses a gear hobbing cutter system with a cutter head body that receives a plurality of supporting blocks (i.e., holders). Each of the holders includes a pocket that receives a cutting insert. The cutting insert is indexable to at least two cutting edges. When one of the cutting edges becomes worn, the cutting insert can be indexed for use of the sharper cutting edge, thereby possibly providing cost savings.
One drawback of the device of the Francis et al. '858 patent, however, is that the cutting inserts may not be adequately supported within the pocket of the respective holder. Forces generated during the formation of a gear may shift the cutting insert relative to the supporting block, thereby causing the work piece to be out of tolerance. For instance, the pocket of the holders is substantially open on one side—the side facing the head of the fastener. Because this side is open, the cutting insert may not be adequately supported and the cutting inset may shift out of tolerance, especially considering the high loads on the cutting insert during the gear manufacturing process.
Accordingly, there remains a need for an improved gear milling tool assembly with a holder that receives a cutting insert. More specifically, there remains a need for an improved gear milling tool in which the cutting inserts are better supported by the holder.